Originally Posted by palmetto rogue
x2 on mlwilliams808. I did exactly the same with a 45gal tank. I never have to fuel up with the 5r attached and the tank has paid for itself with fuel cost savings. I used to leave the ball valve open on my 2011 f250 but now drive a 2015 Silverado 2500hd and an error code was set when the fuel tank gage read full for an extended period. Dealer could not tell me why. So now when the primary 36 gal tank gets low on the road I pull over and open the valve and by the time I get to my destination the primary tank is full and I can close the valve.
From a vehicle performance standpoint, gravity feed fuel systems can adversely affect federally mandated, manufacturer implemented, on-board vehicle diagnostic systems. In the case of many newer vehicles, a gravity fed system keeps the main fuel tank overfull and will likely result in a diagnostic trouble code. In addition to being a nuisance, drivers may miss valid vehicle issues because the check engine light remains on.
Taken from Transfer Flow information. The rest of it here - https://www.transferflow.com/regulations